1) A variable that is held constant while some other variable changes. When different values of a parameter are examined, the parameter distinguishes different functions within a family of functions (e.g., a graph of avoidance behaviour can show avoidance response rate as a function of either RS interval with SS interval as a parameter or SS interval with RS interval as a parameter).

2) Any of a set of physical properties whose values determine the characteristics of a behavior, such as schedule and quantity or quality of reinforcers. Differences in parametric values may influence how rapidly, effectively, safely, constructively, durably, and so on, that a given behaviour changes.